This invention is directed to composite expansion joint systems of the type used to seal expansion grooves between bridge deck sections and the like. Such expansion joint systems typically comprise an assembly of end dams or edge members, resiliently yieldable sealing elements extending longitudinally of the groove in side by side relation, transverse sectional dividers in the form of cross beam structural members interposed between adjacent sealing elements, and underlying support bars extending transversely of the groove and supporting the cross beam structural members. Customarily such joints incorporate either a single support bar system, as exemplified by U.S. Pat. No. 3,482,492, wherein the cross beams all rest on the same support bar at each location and are laterally slidable thereon during expansion and contraction, or an individual or multiple support bar system. The latter is characterized by the provision of a support bar for each cross beam, with only one cross beam bearing on any one support bar, at each location, and each cross beam being fixed to its support bar for movement therewith. Such a system is shown in U.S. Pat. No. 3,604,322.
It is desirable to maintain equidistant spacing between adjacent cross beam structural members and between the end members and the adjacent cross beam structural members, throughout the range of movement contemplated for the joint. This results in an even load distribution, provides uniformity across the joint and avoids unequal stressing of the seal members and of the interlock between the seal members and adjacent beams and edge members. The individual sealing elements are either under compression at all times and therefore exert centering forces on the beams, or may be disposed between adjacent beams and edge members by means of locking lugs so that in the open position little or no forces are exerted by the sealing elements on the system. However, as the bridge deck moves, either by expanding or contracting, it is desirable to maintain equidistant spacing of the cross beams and edge members so as to eliminate the possibility of pulling a sealing member out or of having an esthetically unpleasing arrangement of these members. Therefore it is desirable to supplement the centering action of the sealing elements, or lack thereof, preferably in a manner compensating for the variation in forces exerted by the sealing elements especially during the opening movement.
U.S. Pat. No. 3,430,544 discloses a device for sealing expansion joints in bridge decking including a T-shaped plate having arms sandwiched between layers of neoprene at opposite sides of the joint, and a leg fixed to the arms and projecting upwardly between the decking slabs in the manner of a cross beam. The spaces between the side faces of the leg and the edges of the joint are filled by compressed neoprene which expands when the joint opens. The layers of neoprene at opposite ends of the arms are vertically compressed against the arms which cause these layers to be distorted as the joint opens. U.S. Pat. No. 3,604,322 discloses cross beams interposed between sealing elements and fixed to support bars in an individual support bar system. Elastic elements are vertically compressed against the opposite ends of the support bars, to exert centering forces thereon. In other embodiments, compression springs are positioned between adjacent support bars in a manner exerting centering forces thereon. However, both of these prior art arrangements are applicable only to multiple support bar systems or to expansion joints of the individual support bar type, wherein the cross beams are rigidly connected to the support bars for lateral movement therewith, because the centering forces applied to the support bars would have no effect on cross beams which are laterally slidable on the support bars as in the single support bar system described above.